Field of the Invention
The present invention relates to mobile communication.
Related Art
3rd generation partnership project (3GPP) long term evolution (LTE) evolved from a universal mobile telecommunications system (UMTS) is introduced as the 3GPP release 8. The 3GPP LTE uses orthogonal frequency division multiple access (OFDMA) in a downlink, and uses single carrier-frequency division multiple access (SC-FDMA) in an uplink.
Such LTE may be divided into a frequency division duplex (FDD) type and a time division duplex (TDD) type.
As set forth in 3GPP TS 36.211 V10.4.0, the physical channels in 3GPP LTE may be classified into data channels such as PDSCH (physical downlink shared channel) and PUSCH (physical uplink shared channel) and control channels such as PDCCH (physical downlink control channel), PCFICH (physical control format indicator channel), PHICH (physical hybrid-ARQ indicator channel) and PUCCH (physical uplink control channel).
A carrier aggregation system means aggregating a multiple of component carriers (CCs). The meaning of the existing cell was changed by such a carrier aggregation. According to the carrier aggregation, a cell may mean a combination of a downlink component carrier and an uplink component carrier, or a single downlink component carrier. In the carrier aggregation, a cell may be divided into a primary cell, a secondary cell, and a serving cell.
Meanwhile, in order to process data on the increase, in a next generation mobile communication system, it is expected that a small cell with a small cell coverage diameter is to be added within the coverage of the existing macro cell, and the small cell will process traffic greater than before.
Meanwhile, recently, the technology of enabling dual connectivity to the macro cell and the small cell by a user equipment (UE) is currently studied.
Furthermore, recently, a scheme of applying a dual connectivity technology designed in consideration of base stations at different geographical locations to the carrier aggregation (CA) technology operated by one base station is currently studied. According to this scheme, when the PUCCH resource of a primary cell (PCell) is not sufficient, the whole or partial PUCCH transmission of UEs may be detoured to a specific secondary cell (SCell).
However, a technical ambiguity issue may be generated between the base station and the UE during the time section in which one base station switches to dual connectivity in the carrier aggregation (CA).